120 NITROGEN METABOLISM 



Maschmann observed that the proteinases, but not the 

 specific gelatinase, were inhibited by normal (i.e. not neces- 

 sarily immune) sera. A more recent careful kinetic study of 

 the proteolytic activity of several bacteria disproved the idea 

 that this effect wsls due to the same substance that inhibits 

 trypsin [13]. The trypsin inhibitor is found only in the 

 albumin fraction of the serum proteins, whilst the labile 

 antibacterial protease factor is in the globulin fraction: 

 furthermore, the bacterial enzymes are not inhibited by the 

 trypsin inhibitors present in soya bean, the pancreas and 

 ovomucoid. The antibacterial serum factor inhibited all the 

 bacterial proteases examined, even the specific gelatinases 

 to a small extent. These investigations of Duthie and Lorenz 

 also confirmed that the ability to clot milk is restricted to 

 certain bacteria, and showed that although inhibited by the 

 globulins of normal sera, the rate of clotting bore no relation- 

 ship to the protease activity of the culture filtrates. 



Factors affecting the formation and activity of extracellular 

 proteinases 

 The composition of the growth medium profoundly 

 affects the degree of proteinase activity that is ultimately 

 detectable in the culture filtrate. Three factors appear to be 

 of special significance, (i) inorganic ions, (ii) fermentable 

 carbohydrate and (iii) the organism's source of nitrogen. A 

 previous observation [30] that protease production by a 

 species of Proteus depended on the presence of Ca and 

 Mg"^"^ was investigated in more detail by Hanes, using the 

 organisms Bacillus subtilis, B. mesentericus, Pr. vulgaris, Ps. 

 fiuorescens and Ps. aeruginosa [22]. The addition of Ca^"^ 

 had little effect on grov^h, but markedly increased the pro- 

 duction of gelatinase, whilst Mg"^"*", although increasing 

 growth, caused no increase in the gelatinase activity of the 

 cultures. The recent work of Gorini has served to emphasize 

 the important role of cations such as Ca"^^ [17]. Optimal 

 extracellular protease activity of Micrococcus lysodeikticus, 

 B. megatherium, Proteus, Ps. pyocyanea and B. mesentericus 

 was dependent on growth at a low temperature (26° C.) in 



